1. Field of the Invention
The present invention relates generally to hard copy apparatus and, more particularly, to a method and apparatus for handling wet-print, cut-sheet, media output in order to extend passive drying time before contact occurs between consecutively ejected sheets.
2. Description of Related Art
Because some hard copy apparatus use liquid inks, toners, and colorants (generically referred to hereinafter as "ink") and because output print media sheets--paper, envelopes, card stock, and the like (synonymously referred to hereinafter as "sheets" or "paper")--often are stacked immediately after printing, such wet systems have experienced difficulty with blotting and smearing of ink upon contact between consecutively deposited sheets in the output tray. For example, in a conventional ink-jet hard copy apparatus--such as a computer printer, a copier, a facsimile machine, or the like (synonymously referred to as a "printer" hereinafter)--sheet media are directed through a print cycle which includes picking up a sheet from an input tray, feeding it through the printer's printing station, and then ejecting it through an output port. Once ejected, the sheet usually is deposited in an output tray, consecutive sheets piling one on top of one another to form an output stack. The blotting and smearing problem has been particularly apparent where the ink drying time consistantly exceeds the time between printing of consecutive sheets. These detrimental effects are more pronounced in special print media, such as transparencies and glossy photographic quality papers where drying time is substantially longer than for plain paper.
Although a variety of solutions have been proposed for this problem, providing adequate ink drying time without some cost to the throughput efficiency, versatility, or paper size or composition limitations remains an issue for the system designer. Some printer manufacturers have attempted to eliminate ink smearing and blotting problems by decreasing the ink drying time. One solution has been to employ quick-drying ink. Another has been to employ special paper. Special inks and paper increase the cost of operation for the end-user and optimizing the dry-time factor may compromise other important parameters such as print quality or permanence. Yet another solution has been to provide a separate, active drying device adjacent the paper output path. Providing a separate drying device adds to the complexity and cost of the printer itself. A further solution has been to impose a delay on the deposit of each sheet into the stack to provide the previously printed sheet with adequate drying time. The most basic of such solutions have involved simply slowing printer throughput by creating an artificial time delay between the printing of consecutive sheets. This solution is contrary to the design goals of improving printer efficiency and throughput.
Still another solution has been to employ an ejection path passive drop scheme. A sheet emerging from the printer's output port is guided along the top of rails which suspend the sheet above the output tray. At the completion of printing and release of the trailing edge from the printing station or a downstream paper transport device, the sheet simply drops from the rails of its own weight. This gives the previously printed sheet further drying time. However, passive drop schemes are not always reliable due to cockling of sheets receiving dense print patterns. A cockled sheet may hang up on the rails and thus be pushed forward and out of the printer by the next sheet.
Another solution to the problem involved the use of an ejection path active drop mechanism where an output sheet is guided along the top of a pair of movable wings which temporarily support the sheet above the output tray. At the completion of printing and release of the trailing edge from the printing station or downstream paper transport device, the wings retract, allowing the sheet to fall. Again, the previously printed sheet is provided with extended dry time. Active wing mechanisms add complexity and cost to hard copy apparatus. Moreover, they are generally coupled to fixed pivot mechanisms and thus dictate the width of paper used in the printer. Another phenomenon associated with movable wing mechanism is "sheet sail," where the dropping sheet flies out of the paper as the wings are retracted.
U.S. Pat. No. 5,603,493 by Kieran Kelly (Feb. 18, 1997) for a System for Use in Handling Media teaches a sheet media handling system employing an edge guide mechanism providing a sheet stiffening bowing of an output sheet to hold the sheet above the output tray until released (assigned to the common assignee of the present invention and incorporated herein by reference). The present invention provides improvements on such mechanisms.